The present invention relates to a resin composition for polymerization casting which is useful for preparing an optical material such as a plastic lens, and an optical material having an excellent impact resistance, low specific gravity, and light weight.
Various studies have been made on organic glass as a substitution for inorganic glass. However, organic glass which has hitherto been made has various defects, and thus has never had sufficient properties. Typical example of the organic glass includes polyethylene glycol bis allyl carbonate. Polyethylene glycol bis allyl carbonate is typically used for preparing an optical material such as a plastic lens due to its excellent impact resistance, scratch resistance, castability, dyeability, and adhesivity to a hard coat film. However, polyethylene glycol bis allyl carbonate has refractive index of as low as 1.50, so that, when this compound is used for producing a concave lens (minus lens), the edge thickness of the concave lens (minus lens) becomes thick. Further, polyethylene glycol bis allyl carbonate has specific gravity of as large as about 1.32, so that the lens produced with this compound is heavy. Therefore, it is strongly demanded for an optical lens material to have high refractive index and low specific gravity at the same time. In an attempt to meet the demand, various resins having high refractive index have been proposed.
For example, it is proposed in Japanese Patent Publication Nos. 58-17527 and 3-45362 to produce a synthetic resin lens with a monomer composition containing di(meth)acrylate represented by the formula (3) below ##STR3## wherein R.sup.1 and R.sup.2 each stands for a hydrogen atom or a methyl group, m and n each is an integer of 0 to 2.
However, the mechanical strength and impact resistance of the synthetic resin lens are not yet sufficient.
It is also proposed in Japanese Patent Publication No. 6-93041 to produce a synthetic resin lens with a monomer composition containing di(meth)acrylate compound represented by the formula (4): ##STR4## wherein R.sup.1 stands for a hydrogen atom or a methyl group, R.sup.2 and R.sup.3 each stands for an alkylene group having 2 to 6 carbon atoms, X stands for a hydrogen atom, a chlorine atom, a bromine atom, an iodine atom, or an alkylene group having 1 to 4 carbon atoms, Y stands for an atomic group selected from a straight or a branched alkylene group having 1 to 3 carbon atoms, --O--, --S--, --SO--, or --SO.sub.2 --, m+n is 0 or an integer of 1 to 4, k+l is an integer of 0 to 12.
This publication discloses a variety of monomers wherein Y and k+l vary, respectively, as embodiments of the di(meth)acrylate compound represented by the formula (4). However, homopolymers of these monomers has specific gravity of as large as 1.25 or larger, and insufficient impact resistance. The publication also discloses to mix two or more kinds of the di(meth)acrylate compounds represented by the formula (4), and to combine the compound with other monomers. However, the combinations described specifically in the publication do not have sufficient lightness in weight, heat resistance, impact resistance, or the like.